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Multiferroics permit the magnetic control of the electric polarization and the electric control of the magnetization. These static magnetoelectric (ME) effects are of enormous interest: The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in several multiferroic compounds [1]. In conventional media light propagation is reciprocal, that is counter-propagating beams experience the same refractive index. However, reciprocity can be violated in multiferroic materials, where the refractive index depends not only on the polarization of light but also on the +- k direction of the propagation [1]. Such unidirectional transmission is the consequence of the dynamic magnetoelectric effect emerging in materials with simultaneously broken time reversal and spatial inversion symmetries. This phenomenon, exclusively observed in multiferroic and magnetoelectric materials [2-5], may allow the development of optical diodes transmitting unpolarized light in one, but not in the opposite, direction [5]. Recently, the emergence such unidirectional light propagation, governed the dynamic magnetoelectric effect, has also been demonstrated in multi-antiferroics [6], i.e. in materials with coexisting purely antiferroelectric and antiferromagnetic orders. References [1] D. Szaller et al., Phys. Rev. B 87, 014421 (2014) [2] I. Kezsmarki et al., Phys. Rev. Lett. 106, 057403 (2011) [3] S. Bordacs et al., Nat. Phys. 8, 734 (2012) [4] I. Kezsmarki et al., Nat. Commun. 5, 3203 (2014) [5] I. Kezsmarki et al., Phys. Rev. Lett. 115, 127203 (2015) [6] V. Kocsis et al., arXiv:1711.08124 (2017)

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Istvan Kezsmarki, Uni Augsburg
Seminar Room of the Institute of Physics II
Contact: Joachim Hemberger